Cartoon coyote inspires development of new photonic silicon properties

Microprocessors where information is carried by light beams rather than an electric current inspired by so-called cartoon physics

Nothing can escape gravity, but sometimes it ignores Wile E Coyote. The hapless pursuer of the Roadrunner in Warner Bros classic cartoons is forever running off cliffs and remaining suspended in midair until he realises his predicament and plummets to the canyon floor, raising his characteristic tiny dust cloud. This famous moment of cartoon physics has inspired electronic engineers at Surrey University in the discovery of a new type of silicon that could be used in photonic chips, where information is carried by light beams.

In conventional electronics, silicon is “doped” with other elements to change its electronic properties. The researchers found that the standard elements used for this can control the flow of light with terahertz (Thz) frequency. Previous research has focused on using infrared light, but this has given poor results except with extremely high intensity light.

The researchers were investigating an odd effect seen when two or more photons of terahertz light strike the silicon, as they describe in Nature. Individually, they could go straight through the silicon unhindered, and if they arrive together they get absorbed. The first photon to arrive acts like a switch – its presence or absence determines what happens to the others.

“It’s just like when Wile E. Coyote is chasing the Roadrunner and goes off the edge of a cliff – there’s always a moment before physics wakes up and realises he has too much potential energy and he falls,” said Prof Ben Murdin, who directed the research “During this ‘coyote time’ (as gamers call it) sometimes something else can take effect like a rocket or a stone or a jump.

“That’s exactly how Heisenberg’s Uncertainty Principle works here – there’s a little bit of ‘coyote time’ after the first photon hits in which the molecule doesn’t know what energy it’s supposed to have, but the more energy it tries to ignore the less the coyote time available.”

“We found that with terahertz light silicon’s coyote time is much, much longer, meaning this kind of photon switch is far more efficient than anything else we know of. The results show that silicon may have a completely new lease of life, providing new ways to control information with light rather than electrical current, meaning far faster computers and higher bandwidth communications.”